Various primary batteries employing manganese dioxide as the positive active material such as the carbon-zinc dry batteries, called Leclanche type or zinc chloride type batteries, employing neutral salts of ammonium chloride or zinc chloride as electrolytes, have been well known. Also, alkaline manganese batteries employing potassium hydroxide as the electrolyte, and Li/MnO.sub.2 system primary batteries belonging to organic electrolyte lithium batteries, employing manganese dioxide as the positive active material have been well-known.
On the other hand, lithium-ion secondary batteries which can be high-energy density small size rechargeable batteries in the next generation have also been known. These batteries employ positive and negative electrodes made of a host material repeating intercalation and deintercalation of lithium-ions by charging and discharging, realizing the heavy load discharge, rapid charge, long cyclic life, etc.
Presently, as the host material, a double oxide consisting of cobalt and lithium, or LiCoO.sub.2, is used as the positive electrode, while carbon is generally used as the negative electrode. However, because of the unstable world supply from the high cost and omnipresence of positive electrode material or cobalt, this can now be replaced by LiMnO.sub.2 or LiMn.sub.2 O.sub.4 which are double oxides of manganese and lithium.
As the result of recent power consumption decreases realized by the significant advancement of semiconductor electronics technology, a number of portable electric and electronic apparatuses have been developed and practically used. Various audio visual (AV) apparatuses including the strobe-flash light for still-camera, portable shaver, headphone stereo-player, and liquid crystal display-television (LCD-TV) are typical of these advancements wherein the demand and the use of alkaline manganese batteries having excellent continuous discharge characteristics is now expanding very rapidly.
However, in contrast to these tendencies, increases of power consumption by the multi-functional portable apparatuses have been obvious. For example, in the cases of portable data acquisition (PDA) such as portable telephone and facsimile, notebook personal computer and camcorder, better battery performance taking heavy and continuous loads has been demanded.
Therefore, new built-in type secondary batteries such as the high-capacity nickel-cadmium system, nickel-metal hydride system, or lithium ion type batteries have been developed. At the same time, the demand for alkaline manganese batteries capable of continuous discharge at heavy load working as supplementary power sources is increasing.
When batteries are continuously discharged, decreases of operating voltages due to polarization are generally inevitable in proportion to the increase of load current. Thus, the end voltage is reached before the active materials of positive and negative electrodes are fully reacted so that the ultimate efficiency of active material remains low.
The polarization-based lowering of the operation voltage of discharging cells could be attributed to three reasons, including the resistance polarization due to the electrical ohmic resistance produced in the outer and inner cell, the activation polarization due to the charge transfer reaction, and the concentration polarization due to the diffusion control process of reaction materials or products.
Conventionally, in order to improve the continuous heavy load discharge characteristics of alkaline manganese batteries, the amount of electrolytic manganese dioxide (hereinafter, abbreviated as "EMD") contained in the positive active material is increased, a high conductivity graphite is used as the conductive material in the positive electrode mix, lowering the amount of additives, or a thin separator in which very fine fibers are uniformly distributed is employed.
Other than those discussed above, improvements introducing a gelling agent or a zinc corrosion inhibitor in the negative electrode have been considered effective. In addition to this, the employment of a positive electrode of larger polarization as compared to the zinc in the negative electrode has also been considered.
For example, as shown in U.S. Pat. Nos. 5,277,890 and 5,391,365, methods using EMD powder by expanding its specific surface by forming filament-like protrusions thereon by using a chemical synthetic method precipitating MnO.sub.2 thereon have been developed. In addition to this, a method using a positive electrode to which powder of anatase titanium dioxide is added and mixed as shown in U.S. Pat. 5,342,712 has been disclosed.
Although these inventions have been slightly effective in increasing the battery service-life at continuous discharge and decreasing the polarization compared to a case where a conventional positive electrode made of EMD powder only is used, these had been minimally effective when a heavier load had to be discharged continuously.